The present invention relates to transducer arrays for ultrasound imaging. In particular, two-dimensional transducer arrays for generating images representing two and three dimensions are provided.
Ultrasound imaging for echocardiography applications requires transducers with high volume-per-second rates for scanning. For real-time imaging of moving structures, 20 or more, such as 35, two or three-dimensional representations are generated each second.
Various transducers and associated beamformers have been provided for three-dimensional ultrasound imaging. Currently, mostly mechanical transducers are used. However, the associated imaging is not provided in real time and typically requires ECG gating. Two-dimensional transducer arrays for faster electronic/electronic steering and volume acquisition also have been provided. For example, sparse two-dimensional arrays or fully sampled two-dimensional arrays have been used. Sparse arrays provide poor contrast resolution. Further, the volume-per-second rates for scanning are limited by the speed of sound in the human body and the necessity of having a plurality of ultrasound beams in order to acquire the three-dimensional volume. Likewise fully sampled two-dimensional arrays are also limited by the speed of sound and the necessity of having a plurality of ultrasound beams and require expensive additional beamforming hardware for reducing the number of cables required. As other examples, arrays with beamforming capabilities within a probe or housing for the transducer array are provided. These arrays include walking or rotating aperture two-dimensional arrays, partial beamforming two-dimensional arrays using subarrays, and two-dimensional arrays with time division multiplexing. However, arrays with beamforming in a handle require expensive hardware and are restricted by the same speed of sound limitations.
Two-dimensional arrays repetitively generate transmit beams and responsive receive beams. The beams are electronically steered within the three-dimensional volume. Electronic steering requires a system channel for each of the elements used. Since the number of elements in a two-dimensional array is high, the number of channels required is high. More channels require a greater number of cables. Providing beamforming within the handle of the transducer array may reduce the number of cables required, but the required number of channels and hardware for sampling the two-dimensional array is still high.
Given a volume acquisition rate of 35 fully sampled volumes per second, receiving along four scan lines in response to each transmission, using a single transmit focus over a 90 degree field of view, and for imaging at 40 millimeters of depth, the volume acquisition is limited to about 2000 receive beams. Each transmission takes time. For the acquisition of three-dimensional volumes, the beam width is made larger to account for the limited number of beams while still scanning the whole volume. As a result, the three-dimensional volume is scanned with reduced lateral and elevation resolution. For example, a three-dimensional volume is scanned to a 40 millimeter depth using 44 beams for each scan plane with a xe2x88x926 dB width of 2.9 millimeters for each beam. To increase the resolution, the volumes scanned per-second is decreased, allowing more beams to be used in the same sized volume. Real time three-dimensional imaging is sacrificed for per resolution.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. By way of introduction, the preferred embodiments described below include a two-dimensional transducer array and methods for using the array for two and three-dimensional imaging. A high volume-per-second scan rate using a limited number of system channels (e.g. 192, 256 or other number of channels) is provided by a transducer array without beamforming circuitry in the probe. A fan beam of acoustic energy is transmitted along a scan plane from transducer elements that extend lengthwise over a substantial portion of the lateral aperture. Rows of these long transmit elements are provided along the elevation aperture for electronic steering of the fan beam in the elevation dimension. One or more rows of smaller receive elements are used for forming beams each representing a scan line along the lateral dimension in response to each transmission of a fan beam. Elevation resolution is provided primarily from the elevationally spaced transmit elements and partially from two or more rows of laterally spaced receive elements. The lateral resolution is responsive to the lateral spacing of the receive elements.
In a first aspect, a two-dimensional array for three-dimensional imaging is provided. A first row of the array has at least one first element. A second row of the array is provided adjacent the first row. The second row has at least two second elements. The first element is at least about twice as long in a lateral dimension as each of the second elements.
In a second aspect, an ultrasound system for three-dimensional scanning is provided. A transmit beamformer and a receive beamformer connect to a two-dimensional array of elements. At least a first subset of the elements are connectable with the transmit beamformer, and at least a second subset of the elements are connectable with the receive beamformer. The first subset of elements comprises a greater number of elevation spaced elements than lateral spaced elements, and the second subset of elements comprises a greater number of lateral spaced elements than elevation spaced elements.
In a third aspect, a method for three-dimensional scanning with a two-dimensional array is provided. Acoustic energy is electronically focused in an elevation dimension and transmitted. The acoustic energy has a uniform field in a lateral dimension. At least two beams are electronically focused in the lateral dimension and formed in response to the transmission.
Further aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments.